What do I do if the CRA found an error from my tax return last year and now have reassessed and said I must pay extra tax? Intuit has an accuracy guarantee, right?

Troubleshooting

Yes. This TurboTax FAQ tells you how you can submit a claim under the TurboTax 100% Accurate Calculations Guarantee: https://turbotax.community.intuit.ca/turbotax-support/en-ca/help-article/tax-return/submit-claim-tur...